1. Technical Field
This invention relates to imaging systems, and more particularly to a rear projection dome imaging system.
2. Discussion
Domed imaging systems are used in a variety of applications ranging from entertainment to simulation. Domed imaging visual systems are capable of generating scenes with a high level of realism because the scene is presented to the viewer in many directions at once and not just from a single flat plane as in most conventional imaging systems. This capability of producing a wide field of regard is highly desirable in entertainment systems and is quite necessary in many simulation systems.
Conventional domed imaging systems typically employ front projection techniques. Like conventional movie theaters, these systems employ one or more projectors which are positioned on the same side of the screen as the viewer to project still and/or moving images onto the screen or dome. The dome may consist of a single curved screen or may comprise multiple screens.
Unfortunately, front projection imaging systems have a number of drawbacks. Most obvious are the limitations resulting from the physical and geometrical requirements of such systems. Because the projector and projected light rays are on the same side of the screen as the viewer physical limitations are imposed which restrict placement and movement of the viewer. Further, in simulation and training systems the necessity of avoiding occluding projected light rays places severe limitations on training device location and configuration. In domed visual systems which employ multiple projectors these physical limitations also undesirably restrict the number of projectors, and hence the number of images, that the system can employ.
Another disadvantage with front projection domed systems pertains to the screens themselves. Front projection screens must have a surface with very critical optical characteristics which are necessary to produce sufficient off-axis luminance. Producing screens with these desired characteristics is an expensive process requiring specialized talent to produce the required finish.
Another factor which contributes to the complexity and cost of front projection domed systems is due to the distortions caused by off-axis projection of images onto the curved surfaces. Correcting these distortions requires special video projectors capable of performing such corrections. This requires considerably more expensive projectors and the correction procedures consume a significant amount of time.
An additional correction that is frequently required in conventional domed display systems is due to the interface between adjacent images in multiple image systems. One method of performing this correction is an electronic device which performs a "soft fade" which gradually fades a scene as it begins to overlap to avoid increased brightness from edge portions where images from two projectors overlap. Besides adding to the cost and complexity of the system, "soft fade" techniques only work marginally well in masking the edge effects. Additional corrections are necessary due to off-axis distortions caused by curved screen surfaces. Often this requires expensive video projectors capable of performing such corrections, and edge matching. In addition, domed visual systems having multiple projectors generally require a separate projector and image generation system for each screen, despite the fact that active, or high resolution, images are not required for each channel at the same time.
Thus, it would be desirable to have a domed visual display system in which the placement of a viewer and other equipment is not appreciably restricted by the possibility of occluding projecting images. Also, it would be desirable to have a domed imaging system which does not require complex and expensive correction for edge matching and off-axis distortion correction.
Further, it would be desirable to have such a domed imaging system which utilizes a relatively inexpensive screen material. In addition, it would be desirable to have a domed imaging system providing a wide field of regard, in which edges between adjacent screen panels cannot be detected by the viewer, and which is relatively simple and inexpensive to produce. Finally, it would be desirable to provide a domed imaging system in which an active, or high resolution, image generation system is not required for each screen.